The principal objective of this study is to investigate the mechanism by which pregnancy alters the insulin secretory characteristics of islets of Langerhans. Specifically insulin release has been shown to be increased in response to glucose stimulation in the third trimester in women and in the late stages of pregnancy in rats. This stage of pregnancy is marked by increased nutrient uptake and elevated levels of progesterone, estrogens and placental lactogen. The adenylate cyclase - cyclic AMP system may play a significant role in this enhanced insulin release for the following reasons: the dynamics of insulin release the dose-response to glucose for insulin release and proinsulin synthesis in pregnancy are similar to the effects produced by cyclic AMP on insulin release and synthesis; cyclic AMP content and adenylate cyclase activity are elevated above controls in islets from pregnant rats; cyclic AMP has been shown to manifest its action by stimulation of protein kinases resulting in phosphorylation of cellular proteins; protein kinase activity (both basal and cyclic AMP stimulated) is increased in broken islet preparations from pregnant animals; increased intracellular cyclic AMP in intact islets from control rats has been shown to stimulate specific peptide phosphorylation in a one dimensional SDS-polyacrylamide gel system. It is proposed to compare patterns of protein phosphorylation in intact islets from pregnant rats, from control rats whose islets are treated with agents which raise intracellular cyclic AMP during the phosphorylation process and from control rats. This study will initially be performed with SDS-polyacrylamide slab gel electrophoresis and radioautography of the islets after phosphorylation. In this way quantitative and qualitative differences in substrate phosphorylation may be determined in controls, in controls treated with IBMX and in islets from rats in late stages of pregnancy. The functional significance of specifically phosphorylated substrates to pregnancy and IBMX will then be investigated in relation to the insulin release process. The effect of diet, long term progesterone plus or minus estrogen or placental lactogen therapy on controls will be studied to see if they stimulate the adenylate cyclase-cyclic AMP system as does the state of pregnancy.